Starting an internal combustion engine in low ambient air temperatures, for example below 0° C., is often difficult without the use of starting aids, such as glow plugs. When cold air is drawn into the cylinder of a cold engine, piston velocity needs to be high in order to raise the temperature at top dead centre of the piston cycle and help the fuel in the cylinder to ignite. This is particularly true for diesel engines. However, the piston velocity when starting the engine is dependent on the starter motor alone, which is in turn powered by batteries. Consequently, the starter motor often does not produce a high enough piston velocity to start the engine and the battery may be drained before the engine is able to fire.
Thus, in low ambient air temperatures it is sometimes not possible to start an internal combustion engine, and even when the engine will start, it may take a considerable amount of time to warm up the engine to operating temperatures.
Similar problems may occur at high altitude where the concentration of oxygen in the air is lower than at sea level, and where the ambient air temperature is also low the problems may be even more severe.
The problem may be even more exacerbated if there are any parasitic loads on the engine. For example, if a diesel engine is fitted in a machine, such as a construction or agricultural type machine, the machine may make use of an implement or boom that uses hydraulics to function. Hydraulics require a hydraulic pump to be running, which adds a parasitic load on the engine as the engine starts.
U.S. Pat. No. 7,426,922 describes an engine exhaust gas purifier with an exhaust gas recirculation system (EGR). There are two EGR passages, the first recirculating exhaust gases from downstream of a diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) to a point upstream of the air intake passage to the engine, and the second recirculating exhaust gases from upstream of the DOC and DPF to the point upstream of the air intake passage. Each passage has a throttle valve which may control the volume of gas which passes through the passage. An EGR cooler is also provided partway in the first EGR passage.
The temperature of the air at the intake of the engine is controlled by controlling the throttle valves in the first and second EGR passages to regulate the amount of EGR gas which flows through the cooler in the second EGR passage. The throttle valves are controlled to maintain the air intake temperature within a particular target band, which is predetermined to maintain the DOC and DPF at an efficient operating temperature. The target temperatures tend to decrease as engine loads increase.
Because this system attempts to control the temperature of the DOC and DPF only by passing a proportion of the EGR gas through a cooler before entering the air intake stream of the engine, it cannot heat the DOC and DPF any more rapidly than by passing 100% of the EGR gases through the second EGR passage, where the gases will not be cooled. Therefore, it cannot improve the cold starting of an engine, or more rapidly bringing an engine up to operating temperatures, compared with an engine which has a single EGR passage which is not cooled.